The present invention relates to random number generation. More specifically, the present invention relates to generating random noise/numbers embedded in a semiconductor chip with a reduced operating voltage.
Good cryptography requires good random numbers. Almost all cryptographic protocols require the generation and use of secret values that must be unknown to attackers. For example, random number generators are required to generate public/private key pairs for asymmetric (public key) algorithms including RSA, DSA, and Diffie-Hellman. Keys for symmetric and hybrid cryptosystems are also generated randomly. RNGs are also used to create challenges, nonces (salts), padding bytes, and blinding values. The one time pad—the only provably-secure encryption system—uses as much key material as cipher text and requires that the keystream be generated from a truly random process.
Generating real random numbers has become increasingly vital to information securities, particularly for recent developments in cloud computing, because of its unpredictable pattern suited for the encryption security application. Thus, random number generators have been widely employed from large stationary servers to small mobile devices. However, traditional pseudo-random numbers generated by digital circuits no longer meet the security requirements due to the increasing availability of powerful deciphering computing systems.
It is well known that a zener diode or an avalanche PN junction is a commonly used as the white noise source in discrete circuits. However, at least two challenges must be overcome for the noise source to be implemented in the integrated circuits. First, the breakdown voltage of a discrete zener is quite high, typically about 6V, which is much higher than the maximum operation voltage of the advanced technologies. Second, when the diode is operated in the avalanche mode close to the breakdown condition, the current-voltage curve is very steep. If the voltage is too low, the diode may not enter the avalanche mode. If the voltage is too high, the current becomes very large and the diode could be damaged by breakdown. Although the immediate solution for the discrete zener diode is to enlarge the diode size, it is not feasible in integrated circuits because of the parasitic capacitance concern that will deteriorate circuit performance, cost considerations and reliability concerns.
In prior random noise/number generators, the noise sources are always presented as a block and require external physical noise sources for the circuits. Some noise generators rely on the noise based on physical phenomenon like the thermal noise of resistors.
It is known in the art that a zener diode is a very strong noise source due to the physical nature of its avalanche phenomenon close to the breakdown condition. However, the zener voltage of conventional zener diodes used for random noise generation is about 6V, which exceeds the operation voltage of typical advanced CMOS technologies, for example 1V-2.5V. As zener diodes are p-n junction diodes, increasing p-n junction doping level and abruptness will theoretically result in lower breakdown voltages.
Differential noise pair circuits have been explored previously to cancel out the common cause of variability, such as temperature fluctuation, in order to achieve true white noise sources. Previously used circuits employ one differential circuit for two noise generating blocks. However, they use amplifier circuits in each noise generating block which will distort the noise spectrum because of the limited bandwidth of the amplifiers. Other circuits employ differential circuits on two sources of random noise and then amplify the resulting noise to the level required by voltage comparator. The main drawback of this approach is that the required gain level of amplification is very high (several orders of magnitude) and the resulting reduction in the bandwidth of the amplifier (note that because the product of the gain and the bandwidth of an amplifier is about constant). Such reduction in amplifier bandwidth increases the signal correlation and reduces the randomness of the generated noise.